DISC is a behaviour self-assessment tool originally based on the 1928 DISC emotional and behavioural theory of psychologist William Moulton Marston, which centred on four personality traits: Dominance, Influence, Steadiness, and Compliance. This theory was then developed into a behavioural assessment tool by industrial psychologist Walter Vernon Clarke. Personality expert and researcher, Merrick Rosenberg, notably innovated on the contemporary application of the DISC model as it applies to team development, interpersonal relationships, and American presidential campaigns. DISC has not been scientifically evaluated.
Marston was a lawyer and a psychologist; he also contributed to the first polygraph test, authored self-help books and created the character Wonder Woman. He generated the DISC characteristics of emotions and behavior of normal people (at the time, 'normal' had the meaning of 'typical' rather than an antonym for 'abnormal').
He published his findings in his 1928 book called Emotions of Normal People in which he explained that the four personality types (yellow, green, blue and red) arise as variations between people. According to Marston, people illustrate their emotions using four behavior types: Dominance (D), Inducement (I), Submission (S), and Compliance (C). He argued that these behavioural types came from people's sense of self and their interaction with the environment. He based the four types on two underlying dimensions that influenced people's emotional behaviour. The first dimension is whether a person views their environment as favourable or unfavourable. The second dimension is whether a person perceives themselves as having control or lack of control over their environment.
Although Marston contributed to the theory of the DISC itself, he did not create the DISC self-assessment. In 1956, Walter Clarke, an industrial psychologist, constructed an self-assessment based on Marston's theory. Clarke created the Activity Vector Analysis, a self-checklist of adjectives on which he asked people to indicate descriptions that were accurate about themselves. This self-assessment was intended for use in businesses needing assistance in choosing qualified employees.
Merenda, Peter F. and Clarke published their findings on a new instrument in the January 1965 issue of the Journal of Clinical Psychology." Instead of using a checklist, the "Self Description" test forced respondents to make a choice between two or more terms. Factor analysis of this assessment added to the support of a DISC-based instrument. "Self Description" was used by John Geier to create the Personal Profile System in the 1970s. Geier's DiSC assessment would eventually become Everything DiSC which is now owned by John Wiley & Sons.
DISC has been used to help determine a course of action when dealing with problems as a leadership team—that is, taking the various aspects of each type into account when solving problems or assigning jobs.
Researcher and personality expert, Merrick Rosenberg, extended Marston's research pertaining to the DISC model by applying it to positive organizational leadership and teambuilding. In his books, Taking Flight  and The Chameleon, Rosenberg symbolizes the DISC model into a series of bird characters. He captures the D in the DISC Model to be like an eagle or dominant, decisive, direct, and driven. He captures the I in the model to be symbolized by a parrot who represents the I qualities of being interactive, imaginative, intuitive, and inspirational. He then captures the S to be represented by a dove who is supportive, steadfast, sympathetic, and satisfied. Finally, he represents the C to be a compliant owl who is critical, cautious, and consistent. Rosenberg's findings and application of the DISC model can be found across many companies in the Fortune 100 who utilize his work to develop their culture, organizational cohesion, and leadership strategies. In his book, Personality Wins: Who will Take the White House and How We Know, Rosenberg applies the DISC assessment, and his own methodology, to the personalities of presidential candidates through critical analysis of their campaign rhetoric and leadership communication. His most notable discovery is that leaders are most successful when they adjust their personality communication to comply with the style of their listener.
In 2014, Thomas Erikson wrote a book titled Surrounded by Idiots describing the DISC model and aiming at popularizing it. The book sold over 1.5 million copies worldwide. 
A 2015 report using a sample population of 239,171 people found the following:
Global Overall Population Results(2015): D: 12.3% I: 26.4% S: 30.9% C: 30.4%
Male (Global, 2015): D: 13% I: 28% S: 29% C: 30%
Female (Global, 2015): D: 8% I: 32% S: 33% C: 28%
The report also found different distributions after filtering results by language of the participants. It found a higher percentage of D-types among Russian-speaking participants (23.0%), higher percentage of I-types among participants who spoke German, Italian, and Swedish (48.4%, 46.9%, and 45.6%, respectively); higher percentage of S-types among participants who spoke Chinese, Danish, Finnish, Japanese, Polish, and Taiwanese (44.3%, 47.1%, 43.9%, 40.8%, 40.8%, and 44.8% respectively). This suggests that DISC results are not uniform across the global population but instead heavily differ based on culture.
Inscape Publishing published a 2008 report titled "DiSC Classic Validation Report". The report intends to support the validity and reliability of the DiSC assessment. When testing for test-retest reliability, the report found coefficients between .87 and .89 for retesting after one week, between .73 and .84 for retesting after 5-7 months, and between .71 and .80 for retesting after one year. (A 1 on the scale indicates perfect stability, that is every person who retook the test received the same answer as he/she did before. Having a coefficient above .70 is considered good test-retest reliability). The report found acceptable levels of reliability across genders, race/ethnicities, and age groups.
The report found that the DISC assessment was a reliable assessment, but was criticized for its analysis of validity. Dr. Wendell Williams criticized the report, stating that the 2008 report "reported inter-item reliability — not validity" referring to the fact that the report did not publish findings correlating the DISC to job performance. 
A Russian pilot study found a coefficient of .89 for retesting after one week.
A 2013 report from Wiley examined the construct validity of the Everything DiSC assessment. The report finds results to support the DiSC model's circumplex structure. 
A 2015 report from Extended DISC Global used a sample population of 239,171 people. It found an internal consistency coefficient (Cronbach's alpha) of .84, .82, 83, and .78 for D, I, S, and C types respectively. The 2008 report mentions a 1996 test of internal consistency that yielded coefficients of .92, .87, .85, and .82 for D, I, S, and C types respectively. A Cronbach's alpha of above .70 is considered acceptable, while a coefficient above .8 is considered good.
Some versions of DISC assessments, notably older versions, use ipsative measures. Such assessments would require individuals to choose between two or more distinctly different statements, or would require them to choose words or phrases that describe themselves. These versions can cause issues and do not allow for comparison between different results. The British Psychological Society (BPS) and Chartered Institute of Personnel, Training & Development (CIPD) do not support ipsative tests in recruitment practices. Improved DISC assessments now use a Likert scale in the assessment section to improve accuracy. Other changes include displaying results visually on a grid, graph, or circle model.
Licensed psychologist and psychotherapist Dan Katz, criticised the lack of scientific basis for the model: 'despite the fact that [DISC] has existed for over fifty years and is quite widely spread there is no scientific study [testing its validity]. This means we have no way of knowing if people give consistent answers to the questions over weeks or months. Nor do we have any way of knowing if, for example, a person who answers indicate they are red are in fact dominant or driven.'
R. Wendell Williams, member of American Psychological Association and The Society for Industrial and Organizational Psychology with PhD in industrial psychology, criticizes the practice of using DISC in employee recruitment process. In his criticism, Williams argues that a good job performance test should be well constructed, have test-retest reliability, have Criterion Validity for criteria of job performance, and incorporate the theory of job performance in the test's design. DISC fails the last two points, as it was never designed to be a job performance predictor. Discprofile, one of the vendors of DISC based tests also advises against using the method in employee recruitment. 
Thomas Erikson used the DISC concept as the basis for in his international best-selling book Surrounded By Idiots. He was given the Fraudster of the Year award in 2018 by a critical group Swedish Skeptics. Swedish Skeptics is part of the European Council of Sceptical Organisations (ESCO), a volunteer interest community which "aims to co-ordinate activities of European organisations and individuals that aim at critically investigating pseudoscientific statements and claims regarding observations of paranormal phenomena, and to make the results of its investigations known to the broad public." ECSO's psychologist Dan Katz criticizes Erikson for misleading his audience with unsubstantiated claims of scientific basis for his theory and author's qualifications in the field (Erikson isn't a behavioral scientist his publisher claims him to be).
The content is sourced from: https://handwiki.org/wiki/Social:DISC_assessment